The zebrafish (Danio rerio; Cyprinidae) has become an important model system due to the relative ease of mutational analysis and molecular genetics in this species. This has led to important discoveries of mechanisms and genetic interactions responsible for development of many vertebrate systems. While model systems can of course be quite powerful, the diversity of vertebrate specializations suggest caution must be used before extrapolating from model species to other vertebrates. In the current proposed research, I will examine development of the zebrafish auditory system in comparison to development of the specialized hearing apparatus in the teleost fish American shad (Alosa sapidissima; Clupeidae). One of the shad auditory endorgans (the utricle) is similar to the utricle of the zebrafish early in development but is very different in adults. Unlike most fish, which have a utricular epithelium continuous across the surface, the adult shad utricle exists as three separate pieces with the middle epithelium suspended between the other two by thin connective tissue. This middle epithelium is connected to another hearing specialization called the auditory bulla, a gas-filled chamber that resonates at high frequency. This arrangement has been hypothesized to play a role in the detection of ultrasound, an ability that few other species possess. The focus of the current proposal is to 1) compare development of the utricular macula in shad and zebrafish to determine when and how the utricles of these species differ and 2) examine auditory sensitivity during development in both species to determine how changes in auditory structure may influence auditory function. Comparison of these phylogenetically disparate species should shed light on mechanisms involved in development of the peripheral auditory system and on how epithelial structure affects auditory function.